Various kinds of electrolytes are used for electrochemical devices, such as secondary batteries, electrolytic condensers, electric double-layer capacitors, electrochromic display devices, and dye-sensitized solar cells, among others. Advances in such devices are increasing day by day, and the demands on and the requirements needed for the electrolytes of these advancing devices is likewise increasing.
Currently, the most electrolyte salts used are non-aqueous electrolytes, which are made by dissolving ionizable salts, such as lithium salt, in organic solvents, such as ethylene carbonate, propylene carbonate, dimethoxy ethane, and γ-butyrolactone. However, the use of organic solvents for such non-aqueous electrolytes often leads to leakage issues due to the resulting low viscosity and to vaporization due to their very strong volatility. These organic solvents are also flammable. Therefore, electrochemical devices utilizing electrolytes made using such organic solvents often experience problems with durability and stability.
To solve the flammability of liquid electrolytes in the context of lithium-ion secondary batteries, it has been proposed to use an imidazolium-based or ammonium-based ionic liquid as an electrolyte. However, such ionic liquids may be reduced at a higher voltage than lithium ions in the anode, or imidazolium or ammonium cations may be inserted into the anode together with lithium ions, which deteriorates the performance of the battery.